Cheap and reliable battery pack?

[cwah]

Hello there,

I'm thinkinh of getting a 20s10Ah from this pack:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=26801

They are the cheapest I've found and should be good.

Now I need a reliable BMS for a charge and forget. Where can I find a good BMS?

Thanks

 

[ian.mich]

Hello there,

I'm thinkinh of getting a 20s10Ah from this pack:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=26801

They are the cheapest I've found and should be good.

Now I need a reliable BMS for a charge and forget. Where can I find a good BMS?

Thanks

Yep the hardcases are the best price on RC lipoly in the world. Bestech BMSs have been praised but I'm sticking with non-BMS bulk charge and manually balancing every 50 cycles.
http://bestechpower.com/

 

[cwah]

Thanks ian, I sent them an email for a sample.

I was also using my pack before without bms but I think it as too stressful as I have to stay close to the lipo while charging. Bms would give me peace in mind :lol:

 

[cwah]

Also, anyone know where I can get a 4s to 20s series adapter to plug the batteries to the bms?

Thanks

 

[ian.mich]

Also, anyone know where I can get a 4s to 20s series adapter to plug the batteries to the bms?

Thanks

they include the connectors and wires, you have to hook all your hobby JSTs in parallel then manually connect their loose connector wires. Too bad we cant find someone to make custom BMS connectors so we can buy Methods parallel boards that can just use his jumpers to reach the BMS, no fuss over wiring.

 

[dnmun]

if you decide to use a BMS then there is no need for the JST plugs or the big 10AWG connections. i take the packs apart and assemble them into a regular pack, just like a lifepo4 pack and solder the sense wires directly to the pouches.

but i believe in removing the pouches form the shrink wrap first and then putting the assembled cells in series with a hardboard end plate and then compress them with wood clamps and then wrap the compressed assembly with duck tape to hold it under compression until it blows up.

 

[wesnewell]

I run those in a 24s2p configuration. I made a an adapter balance harness to turn the 6 4s balance leads into 4 6s balance leads so i could balance charge them as 12s4p. It only takes seconds to go from 24s2p to 12s4p and back. All the rc lipo bms's I've seen don't have a suitable LVC, which should be no lower than 3.4V imo, so I would never use one.

 

[cwah]

if you decide to use a BMS then there is no need for the JST plugs or the big 10AWG connections. i take the packs apart and assemble them into a regular pack, just like a lifepo4 pack and solder the sense wires directly to the pouches.

but i believe in removing the pouches form the shrink wrap first and then putting the assembled cells in series with a hardboard end plate and then compress them with wood clamps and then wrap the compressed assembly with duck tape to hold it under compression until it blows up.

That looks like a good idea to have a smaller end on the pack.

Are these the 4s packs from HK? How do you harness everything if you want to double capacity? Let say if you want 10AH instead of 5 AH?

And also how do you monitor your cells life? Do you use the cell log in series for that?

 

[arkmundi]

"Cheap" and "reliable" are mutually exclusive terms. More reliability means more cost. And what do you mean by "reliable?" As long-lasting? As its not RC LIPO so won't catch fire if amped too hard? I believe the proof of time is on the side of those of us paying top dollar for the likes of the A123 AMP20 nano-LiFePO4 cells, because over the long-haul, they are the least cost figured on a charge/discharge basis. I'm still planning on getting 2000+ cycles for 5-10 amp-hours (my current range). And they are NOT prone to fire. And the most environmentally friendly of the various high-C chemistries.

 

[wesnewell]

That old saying 'you get what you pay for' is just BS. What you really pay more for is not always a better product, but for massive advertising budgets to everyone from sports stars to actors, etc. And of course the massive salaries of upper management. Cheaper can be more reliable than expensive. In the case of A123, you're also paying for all their past mistakes and recalls. No thanks. I'll stick with my cheap rc lipo. This month marks one year of use of my $275 24s2p 888wh pack. Still performs as good as new. Into my 3rd year using rc lipo and wouldn't use anything else out there now.

 

[dnmun]

if you decide to use a BMS then there is no need for the JST plugs or the big 10AWG connections. i take the packs apart and assemble them into a regular pack, just like a lifepo4 pack and solder the sense wires directly to the pouches.

but i believe in removing the pouches form the shrink wrap first and then putting the assembled cells in series with a hardboard end plate and then compress them with wood clamps and then wrap the compressed assembly with duck tape to hold it under compression until it blows up.

That looks like a good idea to have a smaller end on the pack.

Are these the 4s packs from HK? How do you harness everything if you want to double capacity? Let say if you want 10AH instead of 5 AH?

And also how do you monitor your cells life? Do you use the cell log in series for that?

i just agreed to build a 24S 16Ah pack for silverheels using these turnigy 8,000mAh nanotech packs. so i can detail that as it happens. initially i will build a harness that connects the sense wires to the cells through the JST plugs and then break the pack in by doing a number of charging cycles enuff to build up the full capacity of the pouches and then test their capacity before committing to build a pack with them or returning them to hobby king if they are short. these 8,000mAh packs are bigger than the 5,000 byt a lot.

he has a dual motored recumbent he rides 27 miles each way to work and so he has to charge at work and he needs the protection of the BMS so i am gonna build his pack around that. he got some aluminum for a case to mount it on the bike. he and i were talking about how to record the cell history. maybe using the 8M cellogs and download the file each day. that would allow insight into the pouches that are going down or self discharge is increasing.

but the guys at bestekpower said they are working on creating a display interface, and i assumed it is based on the D141 since that has recording ability too. but that is limited to 15S. he needs the 24S for the commute to keep in traffic. he says he pulls @28mph over taylors ferry road to beaverton, and that is almost shift down to 4th gear for me in my honda. 5,500 watts through the two motors.

i have no fear of having a fire when using a BMS. there is no risk of overcharging and the BMS provides short circuit protection. it will balance the pack to 4.20 within 5mV sigma. cuts off charge if any cell gets to 4.25 and will cut off the discharge when the first cell hits 2.5V under load. that ends up rebounding to 3V so the LVC is robust but not interfering with the operation. most would never run the pack to exhaustion like i do in testing the BMSs. i have no trouble getting it to balance when i charge it back up. so i can use every bit of storage without risk of damaging the battery. non of that is possible with just balance chargers.

 

[wesnewell]

Hmmm... BMS's are the major causes of fires of lifepo4 battery packs. By the time the first cell gets to 2.5V, all of them will be over discharged since an rc lipo cell is at 0% soc at 3.4V. 30C lipo doesn't sag like lifepo4 pouch cells. All you are going to do with that BMS is ruin a perfectly good bunch of batteries if you run it down until 1 cell is at 2.5V. By then they will all be close to 2.5V. Now if you can set the cutoff at 3.5V, you'd have a workable BMS for rc lipo. Hopefully, his controller will shut off when he reaches 82V. That will save his battery pack. The BMS cutoff sure won't.

 

[dogman dan]

Hogwash. Fires in lifepo4 packs are generally caused by dead shorts, either in wiring, or by a metal item cutting into a pack. Threads about lifepo4 fires are very scarce.

I totally agree though, a lipo bms should be set close to 3.5v. Set it no lower than your usual voltage sag, so 3v -3.4v. Running RC lipo to 2.5v regularly will ruin it fast, and make it risky to charge. I toasted some in 50 cycles doing exactly that. The risk is just higher when dealing with lico, so your lvc should be set to the safer side. Leave that last 5% on the table.

One thing to note, don't smother any bms in foam or other insulating materials that are flammable. That's not a bms causing the fire, it's a moron causing the fire.

BMS or not, only a fool walks off trusting charging inexpensive lico. You don't want to be sleeping in the next room, or worse not present at all.

Get a nice fast charger, so watching it (well, being around and awake) charge takes less time.

 

[dogman dan]

One more note, I like what you are doing with the lipo packs and the bms. But one nitpick, by removing the jst plugs completely, you eliminate an easy way to manually monitor what the bms and the pack are doing.

I'd splice in jst's to the bms wiring harness, so you can still have ports to quickly and easily check cell voltages with a cellog 8. This should be standard for all battery packs in the future, regardless of chemistry of type of bms. Only if the bms itself displays those cell voltages would it not be best to have a port for using a cellog.

Regarding the term cheap. Only when you calculate a projected cost per cycle, or cost per mile can you determine what choice is expected to be cheaper.

But it can be quite convenient to pay less today, which I just did by purchasing 14s 15 ah of new RC lipo, instead of some lifepo4. I know it will need replacing in two years, but hope to be healthy enough to work more by then. My cost per mile will be more than buying another ping would have been, but one advantage is I can run a very strong controller on my cargo bike. To run that cargo bikes big motor, I was going to have to spend twice as much for A123 stuff. The cost per mile won't ever be very low to run that big and powerful bike.

 

[Tommy L]

Hmmm... BMS's are the major causes of fires of lifepo4 battery packs.

Did you mean LiCo?

Tommy L sends.....

 

[cwah]

I think the bms cutoff is 2.5V under load and 4.25 under charge. So when the cutoff happen, the cell should have a resting voltage around 3.5V. It works this way for my lifepo4 BMS, when capacity is low, if I start to pull big amp it just cut the whole battery. But if I pull low amp it works fine..

Dnmun, I have few more questions:
- where do you plan to source the chargers? Bmsbattery that I don't like seem to be the only proven cheap source?
- what lipo charger are you going to use to test the battery capacity? I used to have 2 hyperion but it took forever to test them.
- and of course, I'm looking forward to see how you're going to parallel your pack without making spagetthi or reassembling all the cells

 

[dnmun]

i use a BMS battery charger right now on my 20S pack. i like them. well built and cheap. just the shipping is expensive. i never use balancing chargers.

i test capacity by discharging into a load. i would never use the internal discharger of those balancing chargers. i use 5 1500W electric heaters right now for a load. with a 100V pack i expect it can push 60A.

 

[wesnewell]

I think the bms cutoff is 2.5V under load and 4.25 under charge. So when the cutoff happen, the cell should have a resting voltage around 3.5V. It works this way for my lifepo4 BMS, when capacity is low, if I start to pull big amp it just cut the whole battery. But if I pull low amp it works fine..

Rc lipo doesn't sag near as much as lifepo4 pouch cells do. You can't compare the way they react. Even in a high C rate discharge most recommend an LVC of 3.0-3.1V. The low C rate of an ebike (usually 3C or less) will not let the voltage drop that much from resting voltage.

 

[ian.mich]

I'm sure you could make a BMS with 3.x cutoff. I don't think opening the packs is particularly worth it unless you run 5Ah w/ BMS, or disassemble the packs to solder them in parallel correctly and use BMS, or just want to save space.

 

[el_walto]

http://em3ev.com/store/index.php?route=product/product&path=42&product_id=74

You could try 2 of these for 20s. Not sure if you could then just use one charger?

 

[cwah]

I think the bms cutoff is 2.5V under load and 4.25 under charge. So when the cutoff happen, the cell should have a resting voltage around 3.5V. It works this way for my lifepo4 BMS, when capacity is low, if I start to pull big amp it just cut the whole battery. But if I pull low amp it works fine..

Rc lipo doesn't sag near as much as lifepo4 pouch cells do. You can't compare the way they react. Even in a high C rate discharge most recommend an LVC of 3.0-3.1V. The low C rate of an ebike (usually 3C or less) will not let the voltage drop that much from resting voltage.

It's good news because LVC can be set to 3.0V, perfect for lipo under load
http://bestechpower.com/74v20spcmbmspcbforli-ionli-polymerbatterypack/PCM-D107.html

 

[cwah]

i use a BMS battery charger right now on my 20S pack. i like them. well built and cheap. just the shipping is expensive. i never use balancing chargers.

i test capacity by discharging into a load. i would never use the internal discharger of those balancing chargers. i use 5 1500W electric heaters right now for a load. with a 100V pack i expect it can push 60A.

Damn so bmsbattery is the only option? I still can't swallow the lack of warranty and that they never repaired the broken charger they sent me....

 

[Jason27]

A vast majority of battery fires happen because of improper wiring by the user. Don't have your ebike look like a rats nest with wires sticking out all over the place.

 

[cwah]

I'm sure you could make a BMS with 3.x cutoff. I don't think opening the packs is particularly worth it unless you run 5Ah w/ BMS, or disassemble the packs to solder them in parallel correctly and use BMS, or just want to save space.

Yes it does seem to me that we cells in parallel I would have to scrap the cells from the pack and reassemble them. Not sure if it worth the time to re-wire all connections.

 

[ian.mich]

Damn so bmsbattery is the only option? I still can't swallow the lack of warranty and that they never repaired the broken charger they sent me....

Bms battery, EM3EV, and me